This invention relates to a probe for use in spectroscopy, for example Raman or fluorescence spectroscopy. It also relates to a method of manufacturing a component of such a probe.
Probes for spectroscopic use are known from, for example, U.S. Pat. No. 5,112,127 (Carrabba et al) and U.S. Pat. No. 5,377,004 (Owen et al).
The probes shown in those patents are supplied with laser light via an optical fibre, and the laser light is focused by a lens onto a sample. Resulting scattered light, e.g. Raman scattered light or fluorescence at different wavelengths from the laser, is collected by the lens and fed to a second optical fibre, which takes it to a spectroscopic device for analysis. In the Carrabba patent, the scattered light is folded out of the path of the illuminating laser beam within the probe by a beamsplitter. The Owen patent describes an inverse arrangement, in which the scattered light passes in a straight line through the beamsplitter. The beamsplitter acts to fold the illuminating laser light into this beam path, towards the sample.
In both the Carrabba and Owen patents, the beamsplitter is a dichroic filter. This has several advantages. Firstly, a dichroic filter reflects and transmits the various wavelengths more efficiently than a conventional beamsplitter. Secondly, it rejects Raman scattering or fluorescence caused by the interaction of the intense laser light with the glass of the optical fibre which delivers the laser light, passing only a monochromatic laser wavelength to the sample. Thirdly, it removes much of the laser wavelength which is back-scattered by the sample along with the desired Raman or other scattered wavelengths. Thus, the desired scattered wavelengths do not become confused in the return optical fibre with Raman scattering or fluorescence induced in the optical fibre by the laser wavelength, which as received from the sample is many times more intense than the desired signals. It also makes it easier to separate the desired wavelengths from the laser wavelength in the spectroscopic apparatus.
In some applications, it would be desirable to miniaturise such a probe. One example is where the probe is to be incorporated in an endoscope for medical examinations, where a maximum diameter of 2 mm or less may be desirable. The probes described in the Carrabba and Owen patents comprise numerous discrete components which must be assembled and aligned, making it impossible to achieve such miniaturisation.
The present invention, at least in preferred embodiments, seeks to provide a probe having fewer discrete components.
One aspect of the present invention provides a component for a spectroscopic probe, comprising a block of transparent material, having two opposed angled faces arranged for reflection of light from one to the other within the block. Preferably at least one of said angled faces has a reflecting or partially reflecting coating, e.g. a dichroic filter coating which reflects light of a first wavelength (or range of wavelengths) and transmits light of a second wavelength (or range of wavelengths).
In a second aspect, the present invention provides a spectroscopic probe comprising such a component.
In a third aspect, the invention provides a method of making a component for a spectroscopic probe, comprising the steps of taking a sheet of transparent material, coating at least one face of the sheet of transparent material with a reflecting or partially reflecting coating, e.g. a dichroic filter coating, and cutting said component from the sheet with a cut which is at an angle to said face, thereby producing an angled face with said coating in the resulting component.
The other angled face of the component (opposing the angled face with the dichroic coating) may be coated with a reflecting material, e.g. aluminium. Likewise, in the method according to the invention, the face of the sheet of transparent material which opposes the face with the dichroic coating may be coated with a reflecting material such as aluminium.